Carbon export and the uptake of anthropogenic CO\(_2\) in the Southern Ocean using stable carbon isotopes of dissolved inorganic carbon

The main objective of this research was to investigate and better understand carbon cycling in the Southern Ocean. Measurements of Dissolved Inorganic Carbon (DIC) and its stable carbon isotopes were used to quantify both carbon export and the accumulation and uptake of anthropogenic CO\(_2\) in the Australian sector of the Southern Ocean. To determine carbon export, we measured DIC and δ\(^{13}\)C\(_{DIC}\) on five cruises which cover winter and summer conditions in the sub-Antarctic zone (SAZ), South of Australia. Seasonal variations in mixed layer DIC (45μmol/kg) and δ\(^{13}\)C\(_{DIC}\) (0.45‰) in the region were large. Biological production contributed to about 80% of the winter to summer mixed layer carbon changes in the SAZ with air-sea exchange (10%) and mixing (10%) having smaller contributions. The integrated biological carbon export from the mixed layer from July to February was largest in the northern SAZ (45°S-47°S) at 3400mmol/m\(^2\) and decreased to 1100mmol/m\(^2\) at the sub-Antarctic Front (SAP). The isotopic composition of exported carbon was estimated to be about 18±2‰ and suggests larger phytoplankton drive the seasonal carbon export in the SAZ. Extrapolating the derived carbon export to the circumpolar SAZ gives a total carbon export from July to February of 0.65GTC. To quantify anthropogenic CO\(_2\) accumulation, we compared DIC measurements taken in 1968 to those taken in 1996 using a multi-parametric linear regression technique. For this period, significant accumulation of anthropogenic CO\(_2\) (13±10μmol/kg) was observed in Antarctic Bottom Water (AABW) down to 4500m suggesting AABW is important in transporting anthropogenic CO\(_2\) from the surface to the deep ocean. Very low penetration and accumulation was observed in the Antarctic Zone (AZ) while while the highest accumulation (